Generally, when a driver turns off, the ignition of a vehicle and pulls out a key, an electrical steering column lock has been used to lock a steering wheel 1 (FIG. 1) to thereby prevent the steering wheel 1 from moving. The electrical steering column lock should be configured to prevent the steering wheel and the column shaft from being unlocked even when a torque at or above a predetermined amount is applied to steering wheel 1 and column shaft 2.
FIG. 1 is a perspective view illustrating an apparatus associated with a steering wheel. FIG. 2 is a cross-sectional view taken along the line A-A of FIG. 1 illustrating a column shaft connected with a steering wheel and an electrical steering column lock disposed to lock the steering wheel. FIG. 3 is a perspective view illustrating an electrical steering column lock according to prior art, and FIG. 4 is a diagram illustrating a locked state of the steering column by inserting a lock bar of the electrical steering column lock into a lock ring of the column shaft so as to be locked into a locking projection. As illustrated in FIGS. 1 to 4, steering wheel 1 is connected with the column shaft 2, and column shaft 2 is connected with a steering apparatus of a vehicle to adjust the steering angle according to steering wheel 1 rotation.
Meanwhile, the outside of the column shaft 2 is provided with a lock ring 4, having a slip ring 3 interposed therebetween. An outer surface of the lock ring 4 is provided with a locking projection 42. The lock ring 4 receives a lock bar 57 of an electrical steering column lock 5 so as to interfere with the locking projection 42, such that rotation of the steering wheel 1 and the column shaft 2 is restricted. That is, when the lock bar 57 advances as soon as a driver turns off the ignition of a vehicle, and pulls out a key, the steering wheel is locked in an “OFF” state so as not to move.
The lock bar 57 advances and retreats according to the advancing and retreating of a locking guide 53 that is screw-connected with a worm gear 52, connected with a motor 51, rotating according to rotation of the motor 51 and receiving the worm gear 52. A pin 55 formed on the locking guide 53 is inserted into an elongated hole 58 of the lock bar 57, and an internal spring 56 is inserted between the locking guide 53 and the lock bar 57, such that the lock bar 57 is elastically supported by the locking guide 53, biased toward the lock ring 4.
The reason why an end of the locking guide 53 is not directly inserted into the lock ring 4 and the lock bar 57 is elastically connected with the locking guide 53 is as follows. When the locking projection 42 coincides with the advance position of the lock bar 57 according to the position of the stopping steering wheel 1 and column shaft 2, the lock bar 57 interferes with an upper surface of the locking projection 42 so as to no longer advance, and the internal spring 56 is compressed. When a driver turns the steering wheel 1 to slightly change the position of the locking projection 42 so as to release the interference with the lock bar 57, the lock bar further advances so as to enter a side of the locking projection 42. That is, with the steering wheel 1 in the state in which the ignition of a vehicle is turned off, when the position of the locking projection 42 is not constant, the lock bar 57 does not advance, because it is directly connected with the motor 51, but elastically advances once by way of the internal spring 56.
However, due to the above described structure, the lock bar 57 locks the lock ring 4 with the elastic force by the internal spring 56. In addition, as illustrated in FIG. 4, when the lock bar 57 retreats from the lock ring 4, it is inevitable to develop a chamfer a so as to facilitate undesirable retreat of the lock bar 57. Therefore, when a torque b applied to the steering wheel 1 is larger than a predetermined value, a component of force c is generated in a direction in which the lock bar 57 retreats by virtue of the chamfer a. When the force c is increased and thus overcomes the elastic force of the internal spring 56, the lock bar 57 retreats from the lock ring 4 to cause a jumping phenomenon.
This phenomenon is problematic during a regulatory testing of steering column locking strength. According to regulations on the steering column locking strength, when the slip ring 3 is interposed between the column shaft 2 and the lock ring 4, the column shaft 2 needs to withstand a column rotation torque of 100 Nm or more when the column shaft 2 rotates to the left and right five times by 90°. However, the chamfer a of the lock bar 57 and the locking projection 42 of the lock ring 4 may become deformed during forced rotation of the column shaft 2 to generate a larger component of force c than expected, such that the lock bar 57 jumps from the lock ring 4 before the predetermined torque is applied.
This phenomenon changes according to variations in machining and surface treatment of the lock ring 4 and the lock bar 57 of the steering column. Therefore, the electrical steering column lock cannot be aptly robust and controlled.